Capillary Action (Kimberly Tafoya)

Principles

Demonstrates the dependence of capillary rise upon the diameter of the bore of a tube.

Standards

Include the science standards which are addressed by this equipment. If no specific content stards are addressed, use theinvestigation and experimentation standards.

Materials needed

1. Capillary set

2. Colored water

Procedure

1. Fill lower tray with water.2. Note that the fluid rises higher in the small tubes than the large ones.

Explanation

Capillary action is the result of adhesionand surface tension. Adhesion of water to the walls of a vessel will cause an upward force on the liquid at the edges and result in a meniscus which turns upward. The surface tension acts to hold the surface intact, so instead of just the edges moving upward, the whole liquid surface is dragged upward.

Although this looks to be similar to a capillary tube, this specific capillary tube did not show much differentiation between the tubes during demonstration. It has been suggested that this demonstration equipment would be more suitable for demonstrating the water table levels.

Questions

Why will water rise higher in a smaller tube?

Compare and contrast cohesion and adhesion.

List three examples of where capillary action occurs.

Everyday examples of the principles illustrated

A familiar example of capillary action is the tendency of a dry paper towel to absorb a liquid by drawing it into the narrow openings between the fibers.The movement of groundwater through the soil zone is controlled, in part, by capillary action.

The transport of fluids within plants is also an example of capillary action. As the plant releases water from its leaves, water is drawn upward from the roots to replace it.

Photos

The mutual attractive force that exists between like molecules of a particular liquid is called cohesion. This f

orce is responsible for holding a raindrop together as a single unit. Cohesion produces the phenomenon known as surface tension, which may allow objects that are more dense than th

e liquid to be supported on thesurfaceof the liquid without sinking. When an attractive force exists between two unlike materials, such as a liquid and a solid container, the attractive force is known as adhesion. Adhesion is the force that causeswaterto stick to the inside of aglass. If theadhesiveforce between the liquid and solid is greater than the cohesive force within the liquid, the liquid is said to wet the surface and the surface of the liquid near the edge of the container willcurveupward. In cases where the cohesive force is greater than adhesion, the liquid is said to be nonwetting and the liquid surface will curve downward near the edge of the container.